Greenhouse Gases: How Long Will They Last?

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

In a comment on my Global Warming Crib Sheet, johnmashey asked if I could say something about the lifetimes of greenhouse gases – that is, how long different greenhouse gases stay in the atmosphere. Great idea! Here's a whole post on it.

Many people don't realize that the greenhouse gases we emit can stay in the atmosphere for decades, centuries or even millennia. That's why it's so important that we cap emissions as soon as possible.

Here's a table showing a selection of greenhouse gases, their global warming potential (GWP), and their lifetimes:

Notice that the carbon dioxide lifetime is "hundreds of years", rather than a specific number.

The IPCC Third Assessment Report defines a gas's lifetime as the amount of the gas in the atmosphere divided by the rate at which it is removed from the atmosphere. That sounds simple enough, except that not all gases are removed by just one (or mainly one) process.

Ironically, the gas that accounts for the greatest proportion of global warming, carbon dioxide (CO2), is the hardest to pin down. When CO2 is released into the atmosphere, about three-quarters of it dissolves into the ocean over a few decades. The rest is neutralized by a variety of longer-term geological processes, which can take thousands of years.

About 50% of a CO2 increase will be removed from the atmosphere within 30 years, and a further 30% will be removed within a few centuries. The remaining 20% may stay in the atmosphere for many thousands of years.

My model indicates that about 7% of carbon released today will still be in the atmosphere in 100,000 years. I calculate a mean lifetime, from the sum of all the processes, of about 30,000 years. That's a deceptive number, because it is so strongly influenced by the immense longevity of that long tail. If one is forced to simplify reality into a single number for popular discussion, several hundred years is a sensible number to choose, because it tells three-quarters of the story, and the part of the story which applies to our own lifetimes.

For other gases, a meaningful lifetime is easier to calculate because one process dominates their removal from the atmosphere:

Methane is mostly scrubbed from the atmosphere by hydroxyl radicals (a chemical reaction).

Nitrous oxide is destroyed by photolytic reactions (chemical reactions involving photons or light) in the stratosphere.

As you can see from the chart, some gases have extraordinarily long lifetimes. Because emission rates are vastly higher than removal rates, greenhouse gases are accumulating in the atmosphere and will affect climate for generations to come.

Are there any other climate statistics you'd like to better understand? Post a comment and let us know!

6 Comments

This goes well with your other chart the relative amounts of gasses in atmosphere … fortunately there's a lot less methane than carbon dioxide, and fortunately there's hardly any of the fluorine compounds. I haven't done the math, but if humanity ever gets into a position fo worrying about another ice age, it doesn't look like it takes too much of those to hold it off.

It's also worth noting that while atmospheric chemical reactions take out the methane and nitrous oxide, the rate of removal by the ocean depends on the temperature, and warmer ==> lower CO2 solubility, a positive feedback in the wrong direction.

Maybe the CO2 increasing 100s of years AFTER global warming as shown on ice cores is because the ocean gets warmer and releases CO2. Thus CO2 really doesn't cause the global warming after all. This clarifies it better.

This is my first response to an article here and certainly hope that the science taskers here will listen carefully to any process or information I share as it will be different than what you have been trained to be true.

The earths grid system provides the gases for our eco-system and carbon is the result of a carbohydrate.

A carbohydrate is the result of a plant.

Now why would natural plant material result in the heating or destruction of our eco system.

All of the GHG warming folks have to find a vehicle to support that theory,and it is just their theory.

Grid energy enhancement from processes in the universe have provided the weather anomalies and heating of the magma from grid energy being fed into it.

Its also all about the gravity process on this planet.

Science folks who are not curious enough to seek out grid science are not scientists,they just dont meet the standard definition.

When the grid pressure decreases in a few years and the energy "Globules" that ride on the oxygen lines move out of our galaxy,what will the warming scientists do,will they commit suicide,retire to Bali? Will they be able to return all of the "Knowledge" that has destroyed economies the world over.

All of the diatribes about anyone "Against" the GHG warming specialists being automatically paid for by the oil company is just the Hegelian dialectic model the someone would have you tied to.

As a scientist,you have the responsibility to not make assumptions about someones science theory without a proper inspection of all of the evidence.

I suspect that all of the old science teachers are well retired or gone as that used to be trained into every science tasker.

Grid scientists such as myself are tougher environmentalists than most of the GHG folks,we really are.

But when the earths processes are more understood,folks may be champions for the problems we need to face first.

Excess carbon is a problem for us also as it tasks against the oxygenation balance of the earth.

But the facts are that Jets are responsible for more atmospheric carbon than any other mechanism. Would the industry stop those jets as we have called for and built a complete train system as designed by us??

Here is a statement that I make from time to time that speaks to earths processes and gives a tickle to so many science folks,but is totally true. You can remove every plant on this planet and still breathe for centuries,you just cannot eat.

So Environmental Defense, Im all for it but we have serious problems from what is happening in many areas that needs response from folks with the same energy they have exhibited for climate problems that do not even need fixed,they fix them selves in the respect that the ice will reform when the magma cools,the weather will resume its "Standard" pace and the oil and energy boys will have gotten their way with their energy pricing and the very well planned destruction of the economy.

How many science folks are in favor of their economy being destroyed with their own hands on the haft of the knife??

Much of the CO2 gets reabsorbed into the oceans when the global temperature drops. But when there is global warming, and the oceans release CO2 and extra H2O, the best thing to do is grow crops, and put extra wheat, rye, oats, rice, etc. in sealed cans with CO2 [to prevent it from being eaten] for the day when food becomes scarce. With extra CO2 and H2O, crops grow faster and propagate to increase there ability to absorb CO2. http://NCSDCA.home.ATT.net/opinion/ and select Global Warming.

Russ, In my paradigm, plants that create a carbohydrate in the root system flow the liquid sugar to the plant for its growth processes as fuel.When that fuel is exhausted,a tone opens the stomata or gas pressure opens the stomata by force and exhausts the carbon waste. The plant always has oxygen around it as the aether is connected to the oxygens and seeks ground,therefore plants like trees with roots into the earth become a conductor.

The oxygens flow into the stomata and combine with the exhausted sugar components and make Co2.

So you see,this grid scientist does not agree with the photosynthesis theory as he knows all oxygenation for the planet comes from the gas planet that has the proper speed and tone to provide the oxygens frequency and the sun which also has oxygen lines flowing to it for its frequency burn does not require the geneticists to build a plant that produces any oxygen as it is physically impossible.

Plant biologists had to explain how the planet created all of that fresh air and came up with their theory without any knowledge of how the universe works.

So bottom line is plants have to gas off their waste products,just as we do. So plant biologists ,please gass off your photosynthesis model,it is 2008 and its time.

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